Interpretive Summary: Including dairy foods in the diet may facilitate diet-induced weight loss, possibly by modifying the metabolic effects of the hormone cortisol. This study assessed in overweight women whether inclusion of dairy foods in an energy-restricted diet affects daily cortisol concentrations, and whether person-to-person differences in cortisol concentrations at baseline influence the magnitude of weight loss in response to the diet. Women received either adequate dairy: 3-4 servings of dairy foods per day (AD) or low dairy: =1 serving per day (LD) in a 12-week moderate energy restricted dietary intervention. We found that, on average across all women, energy restriction increased the daily minimum and decreased the daily range in cortisol concentrations from baseline to post-intervention. Energy restriction also enhanced the cortisol response (rise) to eating dinner, but only in LD (this effect was not observed in women consuming adequate dairy). Compared to LD, AD led to a greater loss in body weight and total and upper body fat, but only in women characterized at baseline as having a normal cortisol response to eating dinner (responders); weight and fat lost in AD and LD were similar in those women who did not display a cortisol response to eating dinner (non-responders). Overall, our results suggest that dairy food consumption interacts with some underlying factors related to cortisol regulation to facilitate body weight and upper body fat loss.

Technical Abstract:
Dairy foods enhance weight loss in animal models possibly by modifying the metabolic effects of cortisol. This study aimed to determine in overweight women (ages 20-45; n=51) whether inclusion of dairy foods in an energy-restricted diet affects basal and stimulated cortisol concentrations, and whether baseline differences in provoked cortisol concentrations explain the magnitude of weight loss in response to the intervention. Women received either adequate dairy: 3-4 servings of dairy foods per day (AD) or low dairy: =1 serving per day (LD) in a 12-week moderate energy restricted dietary intervention. Participants were tested in a 12h lab visit, which included a standard breakfast and lunch, and an ad libitum dinner buffet. Salivary cortisol was determined at 10 timepoints across the day from waking to bedtime. Energy restriction increased (P=0.04) the minimum and decreased (P=0.02) the diurnal amplitude in cortisol concentrations from baseline to post-intervention. The dinner-induced rise in cortisol was enhanced (P=0.02) by energy restriction, but only in LD. Compared to LD, AD induced (P=0.04) greater reductions in body weight and total and upper body fat, but only in women characterized at baseline as having a dinner-induced cortisol response (responders); weight and fat lost in AD and LD were similar in non-responders. Overall, energy restriction dampened diurnal cortisol fluctuations (symptomatic of hypothalamic pituitary adrenal (HPA) axis dysfunction) and enhanced dinner-induced cortisol concentrations. However, AD prevented the latter. Furthermore, certain phenotypic markers of HPA axis function may be important for revealing weight-reducing effects of consuming dairy foods.